Scan testing using scan frames with embedded commands

ABSTRACT

Testing of integrated circuits is achieved by a test architecture utilizing a scan frame input shift register, a scan frame output shift register, a test controller, and a test interface comprising a scan input, a scan clock, a test enable, and a scan output. Scan frames input to the scan frame input shift register contain a test stimulus data section and a test command section. Scan frames output from the scan frame output shift register contain a test response data section and, optionally, a section for outputting other data. The command section of the input scan frame controls the test architecture to execute a desired test operation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of prior application Ser. No.16/108,761, filed Aug. 22, 2018, currently pending;

Which was a divisional of prior application Ser. No. 15/622,840, filedJun. 14, 2017, now U.S. Pat. No. 10,088,527, issued Oct. 2, 2018;

Which was a divisional of prior application Ser. No. 15/233,280, filedAug. 10, 2016, now U.S. Pat. No. 9,714,980, issued Jul. 25, 2017;

Which was a divisional of prior application Ser. No. 14/744,767, filedJun. 19, 2015, now U.S. Pat. No. 9,435,860 issued Sep. 6, 2016;

Which was a divisional of prior application Ser. No. 14/081,481, filedNov. 15, 2013, now U.S. Pat. No. 9,091,728, issued Jul. 28, 2015;

Which was a divisional of prior application Ser. No. 13/870,319, filedApr. 25, 2013, now U.S. Pat. No. 8,618,542, issued Dec. 31, 2013;

Which was a divisional of prior application Ser. No. 13/595,297, filedAug. 27, 2012, now U.S. Pat. No. 8,445,908, issued May 21, 2013;

Which was a divisional of prior application Ser. No. 13/217,851, filedAug. 25, 2011, now U.S. Pat. No. 8,283,665, issued Oct. 9, 2012;

Which was a divisional of prior application Ser. No. 12/539,310, filedAug. 11, 2009, now U.S. Pat. No. 8,028,212, issued September 27, 2011;

Which was a divisional of prior application Ser. No. 11/670,241, filedFeb. 1, 2007, now U.S. Pat. No. 7,657,810, issued Feb. 2, 2010;

Which claimed priority from Provisional Application No. 60/765,300,filed on Feb. 3, 2006.

Pending TI patent application TI-60187, Optimized JTAG Interface,includes subject matter which is related to the subject matter of thisapplication. TI-60187 has been assigned to the assignee of thisapplication, and is incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure relates generally to scan testing of integratedcircuits and, more particularly, to a method of scan testing integratedcircuits whereby the scan patterns shifted into the integrated circuitcontain control information that regulate how the scan patterns will beused during the testing of the integrated circuit.

Description of Related Art

Semiconductor manufacturers must test integrated circuits they fabricateto determine which ones are good and which ones are bad. Testing ofintegrated circuits is achieved by having a tester contacts theintegrated circuits and apply test patterns to the integrated circuits.Today more and more integrated circuit testing is being performed by lowcost testers. Low cost testers are achieved primarily in two ways; (1)decreasing the number of test contacts required between the tester andintegrated circuits under test, and (2) including more efficient designfor test circuitry in the integrated circuit for interfacing to thetester and executing tests. Decreasing the number of contacts betweenthe tester and integrated circuits enables more integrated circuits tobe contacted by the tester and tester in parallel. Including moreefficient design for test circuitry in the integrated circuits allowsthe integrated circuits to be tested more quickly over the reducedcontact interface to the tester.

Summary of the Disclosure

The present disclosure provides a test interface and test architecturefor integrated circuits that allows scan testing of integrated circuitsto occur using a reduced contact interface to low cost testers.

DESCRIPTION OF THE VIEWS OF THE DRAWINGS

FIG. 1 illustrates a test arrangement between a tester and plurality ofthe integrated circuit.

FIG. 2 illustrates an integrated circuit in a parallel scan testconfiguration.

FIG. 3 illustrates an integrated circuit in a parallel scan testconfiguration according to the present disclosure.

FIG. 4 illustrates the test architecture of the present disclosurecoupled to parallel scan paths.

FIG. 5 illustrates a shift element of the input shift register and ashift element of the output shift register coupled to a scan path.

FIG. 6 illustrates an example controller of the test architecture.

FIG. 7 illustrates the test operations of the example controller of FIG.6.

FIGS. 8A, 8B, and 8C illustrate the flow of data during each testoperation of FIG. 6.

FIG. 9 illustrates a second example controller of the test architecture.

FIG. 10 illustrates test operations of the example controller of FIG. 9.

FIG. 11 illustrates additional test operations of the example controllerof FIG. 9.

FIG. 12 illustrates the test architecture of the present disclosureusing differential input and output signals for interfacing to thetester.

FIG. 13 illustrates the test architecture of the present disclosureusing a simultaneously bidirectional transceiver (SBT) for interfacingto the tester.

FIG. 13A illustrates the operation of the simultaneously bidirectionaltransceiver circuit interface between a tester and the testarchitecture.

FIG. 14A illustrates a counter circuit being used to provide the framemarker (FM) signal of the test architecture.

FIG. 14B illustrates an external signal being used to provide the framemarker (FM) signal of the test architecture.

FIG. 15 illustrates an integrated circuit with multiple cores each coreincluding the test architecture of the present disclosure.

FIG. 16 illustrates a core's test architecture interfaced to a testervia a JTAG interface.

FIG. 17 illustrates a detail view of the JTAG interface of FIG. 16.

FIG. 18 illustrates multiple core test architectures interfaced to atester via a JTAG interface.

FIG. 19 illustrates a detail view of the JTAG interface of FIG. 18.

FIG. 20 illustrates a core's test architecture interfaced to a testervia a two signal JTAG interface circuit.

FIG. 21 illustrates a detail view of the two signal JTAG interfacecircuit of FIG. 20.

FIG. 22 illustrates multiple core test architectures interfaced to atester via a two signal JTAG interface circuit.

FIG. 23 illustrates a detail view of the two signal JTAG interfacecircuit of FIG. 22.

FIG. 24 illustrates the test architecture of the present disclosureinterfaced to a tester via various types of interfaces.

FIG. 25 illustrates an integrated circuit whereby multiple cores aretested simultaneously according to the present disclosure.

FIG. 26 illustrates multiple cores within an integrated circuit, eachcontaining the test architecture of the present disclosure whereby eachtest architecture is interfaced to a tester via a separate scan inputand a separate scan output.

FIG. 27 illustrates a single core within an integrated circuitcontaining the test architecture of the present disclosure whereby thecore test architecture is interfaced to a tester via multiple scaninputs and multiple scan output.

DETAILED DESCRIPTION OF THE DISCLOSURE

FIG. 1 illustrates a conventional arrangement between a tester 100 and agroup of integrated circuits 102 under tests. As seen each integratedcircuit is contacted 106 by the tester to allow the tester to input andoutput test patterns to the integrated circuit. The integrated circuitscould be integrated circuits formed on a wafer 104, integrated circuitsarranged on a test fixture 104, or integrated circuits arranged within aburn in chamber 104.

FIG. 2 illustrates a conventional way a tester tests an integratedcircuit 200 using parallel scan testing. As seen, the integrated circuit200 is contacted by the tester to input a test enable input 212, scaninputs 1-N 214, a scan clock input 216, and scan control inputs 218, andto output scan outputs 1-N 220. The test enable input from the tester isused to place the integrated circuit in a test mode whereby functionalflip flops are converted into scan paths 1-N 202 which are used to inputstimulus test data 208 to the functional combinational logic 204 of theintegrated circuit, and to received response test data 206 from thefunctional combinational logic 204. In this example, the scan paths andcombinational logic circuits are assumed to be functional circuitsassociated with an embedded core 210 circuit within the integratedcircuit.

When the integrated circuit is in the above described parallel scan testmode, the tester inputs stimulus test data to the scan paths 202 via thescan inputs 214 and receives response test data from the scan paths 202via the scan outputs 220. The scan clock 216 times the operation of thescan paths 202 and the scan control inputs 218 control the scan paths202 to either shift data in and out or to capture response data from thecombinational logic. The operation of parallel scan testing is wellknown in the industry.

As can be seen in FIG. 2, the tester must contact the integrated circuitwith a fairly large number of contacts to execute the parallel scantest. For example, if 16 scan paths are used for testing, the testerwould have to have 32 contacts for the scan inputs and scan outputs, acontact for the scan clock, a number of contacts for the scan control,and a contact for the test enable. While not shown, the tester wouldalso have contacts for power and ground to power up the integratedcircuit. If a plurality of integrated circuits is to be tested inparallel, as shown in FIG. 1, the tester would need the above mentionedcontacts for each integrated circuit.

FIG. 3 illustrates an integrated circuit 300 incorporating the parallelscan test architecture of the present disclosure. The integrated circuitincludes a core circuit 210 which, in test mode, is arranged intoparallel scan paths 202 and combinational logic 204, as described inFIG. 2. The interface of the test architecture includes a test enable212, a scan clock 216, a scan input 302, and a scan output 304. The scaninput 302 is coupled to the input of an input shift register thatcomprises a series connected stimulus test data section 306 and a headersection 308. The scan output 304 is coupled to the output of an outputshift register that comprises a series connected response test datasection 312 and a header return section 314.

The header return section 314 is optional in the test architecture, asindicated by dotted line. The scan clock 216 is coupled to the input ofa controller 310, which controls the operation of the scan paths 202,the input shift register, and the output shift register based on controlinput from the header section 308 of the input shift register. The testenable input is used to enable the controller 310 and to place theintegrated circuit 300 and core 210 into a parallel scan test mode, asdescribed in FIG. 2.

The test enable, scan clock, scan in, and scan output signals areconnected to an external tester. The stimulus data section 306 hasparallel outputs that are coupled to the scan inputs of the scan paths202. The header section 308 has parallel outputs that provide controlinputs 318 to the controller 310. The stimulus data section 306 and theheader section 308 receive control inputs 316 from the controller 310.

The response data section 312 has parallel inputs that are coupled tothe scan outputs of the scan paths 202. The optional header returnsection 314 has parallel inputs that can be loaded with the control 318outputs from the header register to allow sending back the headercontrol information to the tester to allow the tester to verify that thecorrect header control information was received by the controller 310.Alternately, the header return section 314 may load other data signalsfor sending back to the tester via the scan output 304. The responsedata section 312 and header return section 314 receive control inputs316 from the controller 310.

During operation, the input shift register of the test architecturereceives input scan frames of stimulus and header data from the testervia the scan input 302 and applies the received data to the parallelscan path 202 inputs and controller 310 inputs respectively. Also duringoperation, the output shift register sends output scan frames ofresponse and, optionally, header or other data obtained from the scanpaths 202 to the tester via the scan output 304. The controller 310controls the operation of the input and output shift registers and theoperation of the scan paths 202 based on the control 318 inputs from theheader register 308. The input shift register section operates toconvert the serialized input scan frame from the scan input 302 intoparallel test stimulus and header data which is applied to the inputs ofthe scan paths 202 and controller 310 respectively. The output shiftregister section operates to convert the parallel test response dataoutput from the scan paths 202 and any optional parallel data from theheader return section 314 into a serialized scan frame that is output onthe scan output 304.

As can be seen, the interface of the test architecture of FIG. 3 onlyrequires four contacts from the tester, i.e. test enable, scan clock,scan input, and scan output. Thus the interface of the test architectureof FIG. 3 requires significantly less contacts from the tester that doesthe test architecture of FIG. 2. This reduction in tester contacts is aresult of; (1) the serial to parallel conversion of the input scanframes from the scan input 302, (2) the parallel to serial conversionsof the output scan frames on the scan output 304, and (3) the fact thatthe control 318 data to operate the test architecture is contained as aheader within each input scan frame received on the scan input 302.

FIG. 4 illustrates one example implementation of the stimulus datasection 306, header data section 308, response data section 312, andoptional header return data section 314. The stimulus, header, response,and header return sections contain serially connected shift elements408, each shift element including a multiplexer 404 and a flip flop 406which are shown in more detail in FIG. 5. FIG. 5 illustrates theconnection between one shift element 408 of the stimulus data section306, a scan cell 402 of a scan path 202, and one shift element 408 ofthe response data section 312. While one scan cell 402 is shown in FIG.5 it should be understood that a plurality of scan cells 402 willtypically be in a scan path 202. Both FIGS. 4 and 5 should be referencedduring the following description.

The multiplexer 404 of the shift elements of the stimulus 306 and header308 sections has inputs for receiving; (1) a scan input 502, which canbe from the scan input 302 of the integrated circuit or from a scanoutput 508 from another shift element 408, (2) a logic low signal 504,and (3) the output 506 of the shift element's flip flop 406. Themultiplexer 404 of the shift elements of the response and optionalheader return sections has inputs for receiving; (1) a scan input 510from a scan output of another shift element, (2) a scan output 512 froman associated scan path 202, and (3) the output 514 of the shiftelement's flip flop 406. The output of each multiplexer 404 is input tothe data input of the shift element's flip flop 406. The multiplexers404 allow each shift element to be controlled by the controller 310 to;(1) load data (low signal 504, scan path output 512, or data inputs toheader return register 314) into flip flop 406, (2) shift data throughflip flop 406 from the shift element's scan input to the scan output, or(3) hold the present state of flip flop 406.

Each scan path 202 comprise a plurality of conventional scan cells 402which include a two input multiplexer 520 and a flip flop 522. Theresponse input 516 to the scan cell 402 is coupled to a response outputfrom the combinational logic 210 and the stimulus output 518 from thescan cell 403 is coupled to a stimulus input to the combinational logic210. Multiplexer 520 allows the scan cell to load response data intoflip flop 522 or to shift data through flip flop 522. Multiple scancells 402 are connected serially via the scan cell's scan inputs andscan outputs to form a scan path 202.

The controller 310 has a command (CMD) 410 and frame marker (FM) 412input from the header section 308, and a clock input for the scan clock216. The CMD and FM inputs are signals on control bus 318 of FIG. 3. Thecontroller 310 has outputs for a serial scan enable (SSE) signal, aparallel scan enable (PSE) signal, a clock 1 (CK1) signal, and a clock 2(CK2) signal on control bus 316. The SSE, PSE, and CK1 signals from thecontroller are input to the input shift register's stimulus 306 andheader 308 sections and to the output shift register's response 312 andheader return 314 sections. The SSE, PSE, and CK1 signals control theoperation of the input and output shift registers. The PSE and CK2signals from the controller are input to the scan paths 202 via controlbus 316. The PSE and CK2 signals control the operation of the scan paths202.

At the beginning of each scan frame input to the stimulus 306 and header308 sections, the flip flops of shift elements 408 are set low by themultiplexer selecting the low logic signal inputs 504 to be loaded intothe flip flop. The first bit of the input scan frame is the frame marker(FM) bit 412 and it will be set to a logic high level. By initializingthe shift elements 408 of the stimulus 306 and header 308 sections tologic lows, the controller 310 can easily detect the occurrence of theleading logic high FM bit which indicates that the stimulus 306 andheader 308 sections of the input shift register have been loaded withthe input scan frame. In response to detecting the logic high FM bit,the controller 310 executes a command as determined by the logicalsetting of the scan frame command (CMD) bit 410. This process of settingthe shift elements of the input shift register low, inputting a scanframe to the input shift register with a leading logic high FM bit,detecting the occurrence of the logic high FM bit, and executing acommand in response to the detecting is repeated during the test.

FIG. 6 illustrates one example implementation of controller 310. Thecontroller includes a state machine 602 and a pair of And gates 604 and606. The state machine inputs the CMD 410 and FM 412 signals from headersection 308, and the scan clock 216 and test enable 212 signals. Thetest enable 212 input enables the operation of the state machine, scanclock 216 input times the operation of the state machine, the CMD 410input provides instruction input to the state machine, and the FM input412 indicates when a complete input scan frame has been received in theinput shift register. The state machine outputs the SSE and PSE signalsto control bus 316 and a CK2ENA signal. And gate 604 inputs the CK2ENAsignal and the scan clock 216 signal and outputs the CK2 signal oncontrol bus 310. And gate 606 inputs the scan clock 216 signal and thetest enable signal 212 and outputs the CK1 signal on control bus 310.

FIG. 7 illustrates the operation of the controller 310 of FIG. 6 whenthe test enable signal 212 is set high. The operations include; a serialshift operation 702, a parallel shift operation 704, and a parallelshift then capture operation 706. During a serial shift operation 702,the SSE output is set high and the CK1 operates with the scan clock 216.The serial shift operation is used to input scan frames to the inputshift register sections 306 and 308, and to output scan frames from theoutput shift register sections 312 and 314, as shown in dotted line inFIG. 8A. During a parallel shift operation 704, the CK1 output continuesto operate with the scan clock and the PSE and CK2ENA outputs are sethigh for one scan clock to generate a single CK2 output signal. Theparallel shift operation is used to perform a single shift operationthat shifts data from the stimulus section 306 of the input shiftregister to the scan paths 202 and data from the scan paths 202 to theresponse section 312 of the output shift register as shown in dottedline in FIG. 8B. The parallel shift operation also shifts logic lowsinto the shift elements 408 of the input shift register. If the headerreturn section 314 of the output shift register is used, the singleshift of the parallel shift operation also shifts data from the headersection 308 of the input shift register to the header return 314 sectionof the output shift register, also as shown in dotted line in FIG. 8B.During a parallel shift then capture operation 706, the CK1 outputcontinues to operate with the scan clock, the PSE and CK2ENA outputs areset high for one scan clock which produces a first CK2 output thatperforms the parallel shift operation shown in FIG. 8B, then the PSE isset low while the CK2ENA remains high for an additional scan clock whichproduces a second CK2 output that performs a response capture operationthat loads response data from combinational logic into the scan paths202 as shown in dotted line in FIG. 8C.

As seen in the timing diagram of FIG. 7, the state machine operatesbetween the serial shift operation 702 and the parallel shift operation704, using an inner loop 708, until the scan paths 202 require only onemore parallel shift to be filled with stimulus and emptied of response.When this condition occurs the state machine enters an output loop 712,by way to transition 710, which includes performing a last serial shiftoperation 702 followed by performing a parallel shift then captureoperation 706. After completing the parallel shift then captureoperation 706, the state machine returns to the serial shift operation702 and repeats the above described operation sequences.

In the timing diagram it is seen that when a FM signal 412 occurs, thestate machine interprets the logic level of the CMD signal 410 todetermine the operation to be performed. In this example, a logic low onCMD signal 410 causes the state machine to operate in the inner loop708, and a logic high on CMD signal 410 causes the state machine tooperate in the outer loop 706.

FIGS. 9, 10 and 11 are shown in illustrate that a plurality of CMD bitsmay be used within an input scan frame to enable the controller's statemachine to be commanded to perform a wider variety of test operations.To increase the number of CMD bits, the header section 318 of the inputshift register simply needs to be augmented with an additional shiftelement 408 for each additional CMD bit added to the input scan frame.

FIG. 9 illustrates an example controller 310 which is similar to thecontroller 310 shown in FIG. 6 with the exception that the controller'sstate machine 902 is designed to receive two CMD bits inputs (CMD0 andCMD1) from the header section 308 of the input shift register. The CMD0and CMD1 bits enable the controller's state machine to perform the testoperations previously described in regard FIGS. 6 and 7 (i.e. the serialshift operation 702, the parallel shift operation 704, and the parallelshift then capture operation 706) and additional test operations.

FIG. 10 illustrates the timing diagram of the state machine 902operating in the previously described inner loop 708 in response toCMD1:CMD0 bits being 0:0 when the FM goes high, and entering the outerloop 712, by way of transition 710, in response to the CMD1:CMD0 bitsbeing 0:1 when the FM goes high. The test operations performed in FIG.10 are the same as in FIG. 7. The only difference is that the statemachine 902 of controller 310 performs the test operations in responseto two command bit inputs instead of one command bit input.

FIG. 11 illustrates the timing diagram of the state machine 902operating in the previously described inner loop 708 in response toCMD1:CMD0 bits being 0:0 when the FM goes high, and entering the outerloop 712, by way of transition 710, in response to the CMD1:CMD0 bitsbeing 1:0 when the FM goes high. As seen, the outer loop 712 of FIG. 11includes a new operation 1102 referred to as parallel shift then 2captures as a result of the CMD1:CMD0 bits being 1:0. The new operationdoes two back to back response capture operations instead on the singleresponse capture operation of operation 706 of FIGS. 7 and 10.Performing back to back capture operations is commonly used in theindustry as a way of testing timing sensitive paths between stimuluspatterns input to combinational logic and resulting response patternsoutput from combinational logic.

The state machine may similarly use the remaining decode of theCMD1:CMD0 bits from the header section 308, in this example 1:1, toprovide any other desired test operation. While the controller 310examples of FIGS. 9-11 can decode two command bits into four differenttest operations, additional test operations can be defined and decodedby simply increasing the number of command bit inputs to the statemachine 902 of controller 310. Further while the examples of FIG. 9-11used particular decodes of the command bit inputs to achieve the testoperation, any decode of the command bits may be used to achieve thetest operations.

FIG. 12 illustrates an integrated circuit 1200 including the testarchitecture of the present disclosure. The test architecture is thesame as the test architecture previously shown and described in regardto FIG. 3 with the exceptions that; (1) the internal scan input to theinput shift register sections 306 and 308 is externally provided bydifferential scan input signals 1202 that drive a differential inputbuffer 1203, and (2) the internal scan output from the output shiftregister sections 312 and 314 is provided externally by differentialscan output signals 1204 that are driven by a differential output buffer1205. Use of differential scan input 1202 and scan output 1204 signalsprovide improved noise immunity to the scan input frame data to the testarchitecture from the tester and the scan output frame data from thetest architecture to the tester. Also using differential scan input 1202and scan output 1204 signaling between the test architecture and testerallows the tester to increase the data rate (bandwidth) of the scanframe input to the test architecture and the scan frame output from thetest architecture, which decreases the amount of time it takes toperform the parallel test operation on core 210.

To improve noise immunity and operational frequency of the scan clock216, the scan clock 216 can be replaced, as the scan input 302 and scanoutput 304 were replaced by differential scan inputs and scan outputs,by differential scan clock inputs 1206 that drive the internal scanclock of the test architecture via a differential input buffer 1207. Useof the shown differential scan inputs, scan outputs, and scan clockinputs allows the tester to send and receive scan frames to and from thetest architecture at much higher data rates than would be possible usingthe single ended scan input, scan output, and scan clock signaling ofFIG. 3. Any type of differential signaling may be used in the example ofFIG. 12, however low voltage differential signaling (LVDS) wouldprobably be the most commonly used type of differential signaling due toits high speed operation and low power consumption attributes.

FIG. 13 illustrates an integrated circuit 1300 including the testarchitecture of the present disclosure. The test architecture is thesame as the test architecture previously shown and described in regardto FIG. 3 with the exception that the scan input 1306 to the input shiftregister sections 306 and 308 and the scan output 1308 from the outputshift register sections 312 and 314 is provided by a single externalsimultaneously bidirectional scan input/output signal 1304, via asimultaneously bidirectional transceiver (SBT) circuit 1302. The SBT1304 is a known interface circuit that has a unidirectional input, inthis example scan output 1308, a unidirectional output, in this examplescan input 1306, and a bidirectional input/output channel, in thisexample simultaneously bidirectional scan input/output 1304. The SBT'sunique feature of being able to use a single channel to simultaneouslytransfer the unidirectional input 1308 and unidirectional output 1306signals on the bidirectional input/output signal channel 1304 is bestdescribed using FIG. 13A.

In FIG. 13A, the four cases of SBT signal transfer (A, B, C, D) areshown between a tester and the test architecture within an integratedcircuit. Case A shows the tester outputting a logic low to signal 1304via an SBT and the test architecture outputting a logic low to thesignal 1304 via an SBT. In response to the low outputs from the testerand test architecture, signal 1304 is low which causes the tester andtest architecture to input logic lows. Case B shows the testeroutputting a logic high to signal 1304 via an SBT and the testarchitecture outputting a logic low to the signal 1304 via an SBT. Inresponse to the high output from the tester and the low output from thetest architecture, signal 1304 is driven to a mid-voltage level betweenhigh and low. In response to the mid-voltage level on signal 1304, thetester inputs the logic low from the test architecture and the testarchitecture inputs the logic high from the tester.

Case C shows the tester outputting a logic low to signal 1304 via an SBTand the test architecture outputting a logic high to the signal 1304 viaan SBT. In response to the low output from the tester and the highoutput from the test architecture, signal 1304 is driven to amid-voltage level between high and low. In response to the mid-voltagelevel on signal 1304, the tester inputs the logic high from the testarchitecture and the test architecture inputs the logic low from thetester. Case D shows the tester outputting a logic high to signal 1304via an SBT and the test architecture outputting a logic high to thesignal 1304 via an SBT. In response to the high outputs from the testerand test architecture, signal 1304 is high which causes the tester andtest architecture to input logic high. More detail descriptions of theoperation of SBT circuits are well documented in the industry.

Use of the SBT circuitry enables the tester to access the testarchitecture for scan frame input and output operations using only asingle external signal connection 1304, which further reduces the numberof contact signal between the tester and test architecture within theintegrated circuit. In addition to reducing the number of contacts, theSBT scan frame input and output signaling rate over signal path 1304 canbe equal to or even greater than the scan frame signaling rate using theunidirectional scan input 302 and scan output 304 signals of FIG. 3.

In the description of the disclosure thus far, the FM 412 signal fromheader section 308 has been described as the signal that causes thecontroller 310 to execute a command based on the logic levels of the CMD410, 904, 906 signals. It should be understood the FM signal may comefrom another source other than the header section 308. For example, theFM signal may come from the tester via an additional external input tothe test architecture. Alternately, the FM signal could come fromanother type of circuit within the integrated circuit, such as thecounter circuit described in FIG. 14A.

FIG. 14A illustrates a counter circuit 1406 within the integratedcircuit being used to produce a frame marker (FM) signal 1404 tocontroller 310 to cause the controller to execute a command based on theCMD inputs 1408 from the header section 308. The structure and operationof the test architecture is the same as previously described with theexception that; (1) a counter 1406 has been added to generate the FMsignal 1404, (2) the header section 308 does not include a shift element408 for the FM signal, and (3) the control input of the controller 310that received the FM signal 412 of FIGS. 3, 4, and 6 now receives the FMsignal 1404 from the counter 1406. The operation of the testarchitecture of FIG. 14 can be represented by the timing diagram of FIG.6 by simply replacing the FM signal 412 of FIG. 6 with the FM signal1404 of FIG. 14. At the beginning of the test, the counter is loadedwith a count value representing the bit length of the stimulus 306 andheader 308 sections of the input shift register, which is the input scanframe bit length.

Following the counter load operation, a serial shift operation 702starts to input the input scan frame and output the output scan frame.With the SSE high and scan clocks 216 applied, the counter counts down(CD) each time a scan frame bit is shifted into the input shiftregister. When the counter goes to a count of zero (CZ), the counteroutputs the FM signal 1404 that indicates that a complete input scanframe has been shifted into the stimulus and header sections of theinput shift register. In response to the FM signal, the controller 310executes a command based on the logical settings of the CMD bits 1408from the header section 308. The command can be to execute thepreviously described parallel shift operation 704, the previouslydescribed parallel shift then capture operation 706, the previouslydescribed parallel shift then 2 captures operation 1102, or any otherdefined test operation. Following the execution of the test operation,the controller performs a serial shift operation 702 to input the nextinput scan frame and output the next output scan frame.

In response to the FM 1404 input, the controller sets the PSE signalhigh for one scan clock 216 which causes the counter to reload (LD) thecount value for the next scan frame input and output operation thatoccurs during the serial shift operation 702. While a count down counterwas used in this example, a count up counter or any other type ofcircuit that can count or otherwise determined when the correct numberof scan frame bits have been shifted into the input shift register maybe used as well.

FIG. 14B is provided to illustrate an integrated 1401 in which the FMsignal to the controller 310 is externally input from the tester via anexternal FM input signal 1405. The structure and operation of the testarchitecture of FIG. 14B is identical to that of FIG. 14A with theexception that the counter of FIG. 14A has been deleted and anadditional external input to the test architecture is provided to allowthe tester to input the FM signal 1405 to cause the controller 310 toexecute the command 1408 from header section 308. The alternate FM inputtechniques shown in FIGS. 14A and 14B may be used in place of inputtingthe FM from header section 308 of FIG. 4 in any of the testarchitectures described herein.

FIG. 15 illustrates an integrated circuit 1500 that includes a pluralityof cores 1502-1506 each including the test architecture of the presentdisclosure. Each core test architecture is interfaced to the tester viathe scan input 302, scan output 304, and scan clock 216 signals. Eachcore test architecture is interfaced to the tester via a unique testenable 212 signal (1-N) to allow the tester to enable one of the coresfor testing while the other cores are not tested. As seen, each coretest architecture has a tristate output buffer 1508 to allow the outputshift register of the enabled core test architecture to output responsedata to the tester via the scan output signal 304. The testing of theintegrated circuit's cores occurs one at a time by the tester enablingand testing a first core, then enabling and testing a second core, andso on.

While the scan input 302, scan output 304, scan clock 216 and testenable 212 signals of the test architecture have been described as beingexternally accessible by a tester, there may be times when these signalsare internal signals that are accessed by another set of test interfacesignals. FIG. 16-19 illustrates examples of accessing the scan input,scan output, scan clock, and test enable signals of the testarchitecture via the standard IEEE 1149.1 (JTAG) test access port (TAP),which is a very common and widely used integrated circuit testinterface.

FIG. 16 illustrates an example of an integrated circuit 1600 having aJTAG circuit 1614 interfaced to a core 1602 that includes the scan input(SI) 302, test enable (TE) 212, scan clock (SC) 216, and scan output(SO) 304 interface of the test architecture of the present disclosure.The JTAG circuit has external signal leads for a test data input (TDI)1604, test mode select (TMS) 1606, test clock (TCK) 1608, test dataoutput (TDO) 1610, and test reset (TRST) 1612. During test, theseexternal signal leads are coupled to a tester. Internally, the JTAGcircuit is coupled to the SI, TE, SC, and SO signal of the testarchitecture. Testing of the core is achieved by the tester operatingthe external JTAG signal leads to access the core's test architecturevia the internal SI, TE, SC, and SO test interface signals.

FIG. 17 illustrates the JTAG circuit 1614 in more detail. The structureand operation of the JTAG circuit is well known in the industry. TheJTAG circuitry includes a TAP 1702 controller which enables serialaccess to either the instruction register (IR) 1704 or a selected dataregister (DR) 1706. When the IR 1704 is accessed, serial data is scannedinto the IR via the TDI input and serial data is scan out of the IR viathe TDO output. When a DR 1706 is accessed, serial data is scanned intothe DR via the TDI input and serial data is scan out of the DR via theTDO output. Multiplexers 1708 and 1710 are controlled by the JTAGcircuitry to allow the IR or selected DR output to drive the TDO duringaccess.

As seen, the SI input of the test architecture is coupled to the TDIinput, the TE input of the test architecture is coupled to an outputfrom either the IR or DR, and the SC of the test architecture isselectively coupled, by a new circuit 1714 added to the TAP controller,to the TCK input. To prepare for testing the core, the IR is scanned toload a core test instruction that sets a core test enable (CTE) signal1712 high and selects the SO of the test architecture to be input tomultiplexer 1708 via multiplexer 1710. If the TE signal comes from theIR, it is also set high by the core test instruction to enable the corefor testing. If the TE signal comes from a DR, the DR will be scanned toset TE high prior to loading the core test instruction into the IR. TheCTE signal is input to the new circuit 1714 of the TAP controller, whichin this example is a three input And (A) gate.

After the core test instruction has been loaded, the TAP controller goesto the Shift-DR state, which is the state that enables data to beserially input to the selected DR on TDI and output from the selected DRon TDO. In this case, the data input on TDI, which is the input scanframe, will be input to the test architecture's input shift registersections 306 and 308 and the data output on TDO, which is the outputscan frame, will be output from the test architectures output shiftregister sections 312 and 314. While the TAP controller is in theShift-DR state, a logic high signal will be input to the Shift-DR Stateinput of the And gate 1714. With the Shift-DR State input high and theCTE input high, the And gate 1714 is gated on to allow the TCK input todrive the SC input of the test architecture.

With the JTAG circuit 1614 setup as described above, the SC input of thetest architecture is driven by TCK, input scan frames are input to thetest architecture's input shift register via the connection between TDIand SI, and output scan frames are output from the test architecture'soutput shift register via the connection formed between SO and TDO. TheTAP controller remains in the Shift-DR state until all input and outputscan frames required to test the core have been streamed into and out ofthe core's test architecture. After the test has been completed, the TAPcontroller transitions from the Shift-DR state, which sets the Shift-DRState input to And gate 1714 low, gating off the test architecture's SCsignal from the JTAG TCK signal.

The above described test architecture scan framing input and outputoperation occurs continuously while the TAP controller 1702 is in theShift-DR state, which reduces the time to test the core. If desired, theJTAG circuit 1614 may be designed to perform scan frame input and outputoperations in a non-continuous mode by cycling the TAP controllerthrough its DR shifting states (i.e. Select-DR, Capture-DR, Shift-DR,Exit1-DR, and Update-DR states) to load an input scan frame and unloadan output scan frame then transitioning the TAP controller to theRunTest/Idle state to execute the command in the input scan frame.During the RunTest/Idle state, the JTAG circuit will be designed toallow the TCK to drive the SC input of the test architecture to executethe command. Circuit 1716 comprising And (A) and Or (0) gates can besubstituted for circuit 1714 to enable this alternate method by allowingTCK to drive the SC to input and output a scan frame during the Shift-DRstate, then allowing the TCK to drive the SC to execute the commandduring the RunTest/Idle state. However this alternate method ofinputting and outputting a scan frames is less efficient than justremaining in the Shift-DR state and continuously inputting andoutputting the scan frames since time must be taken to cycle the TAPcontroller through its DR shifting and RunTest/Idle states.

FIG. 18 illustrates an integrated circuit 1800 with a JTAG circuit 1802being used to access the cores 1-N 1502-1506 of FIG. 15 for testing. TheJTAG circuit 1802 is the same as the JTAG circuit 1614 of FIG. 16 withthe exception that the JTAG circuit 1802 has a separate TE (1-N) signal212 for each core 1-N, which allows each core 1-N to be individuallyenabled and tested. In the integrated circuit of FIG. 15, testing Ncores required the tester to provide N separate test enable inputs tothe integrated circuit. In the integrated circuit of FIG. 18, the testeronly needs to provide the JTAG interface signals to the integratedcircuit since the test enable signals are internally provided by theJTAG circuit 1802.

FIG. 19 illustrates the JTAG circuit 1802 in more detail. As with thesingle TE 212 of FIG. 17, the separate core TE's 212 of FIG. 19 may comefrom either the IR 1704 or a DR 1706 of the JTAG circuit 1802. Once acore has been enabled, by setting its TE input high, the core can betested as described in FIG. 17 by either inputting and outputtingcontinuous scan frames while the TAP controller is in the Shift-DR stateor by inputting and outputting one scan frame at a time by cycling theTAP controller through its DR shifting and RunTest/Idle states. Thecores not enabled will have their SO outputs tristated by buffer 1508 ofFIG. 15 to allow only the enabled core to drive the SO 304 input to theJTAG circuit 1802.

FIG. 20 illustrates an example of an integrated circuit 2000 having theJTAG circuit 1614 interfaced to a core 1602 as described previously inregard to FIG. 16. The TDI, TMS, TCK, TDO, and TRST interface signals ofthe JTAG circuit 1614 are interfaced to a serial to parallel controller(SPC) circuit 2002. The SPC 2002 has an external data input/output (DIO)signal 2004 and an external clock (CLK) signal 2006 which are connectedto a tester. The SPC circuit 2002 allows the tester to communicate withthe JTAG circuit 1602 using only the DIO and CLK signals.

FIG. 21 illustrates in more detail the SPC circuit 2002 of FIG. 20. Thestructure and operation of SPC circuit 2002 is described in detail inregard to TI patent application TI-60187, which is incorporated hereinby reference, so only a brief description of SPC circuit 2002 will begiven. As described in the referenced patent TI-60187, the SPC circuitconsists of a data input/output (I/O) circuit 2004, a master reset andsynchronization (MRS) circuit 2006, a controller 2008, a power on reset(POR) circuit 2010, a TAP state machine (TSM) circuit 2012, a serialinput parallel output (SIPO) circuit 2014, and a register 2016 allconnected as shown. The I/O circuit 2004 is simply the SBT circuitdescribed earlier in FIGS. 13 and 13A.

The MRS circuit 2006 is responsible for holding the SPC 2002 andconnected JTAG circuit 1614 in a reset state when no tester is connectedto the DIO and CLK signals and for synchronizing the operation of theSPC with the tester when they are first connected. The controller 2008is driven by the CLK input and provides an update clock (UCK) toregister 2016 and a TCK to the JTAG circuit 1614. The POR circuit 2010is used for resetting the SPC when power is first applied to theintegrated circuit 2000. TSM circuit is used to track the states of theTAP controller in the JTAG circuit 1614. The SIPO circuit 2014 convertsserialized 2-bit data packets input on DIO 2004 into parallel TDI andTMS signals to register 2016. The register 2016 stores the parallel TDIand TMS signal outputs from the SIPO 2014 and inputs them to the JTAGcircuit 1614.

During operation, the I/O circuit simultaneously inputs and outputs dataon the DIO signal, as described previously in regard to the SBT of FIGS.13 and 13A. The data input on DIO is shifted into the SIPO and output tothe JTAG 1614 circuit's TDI and TMS inputs via the register 2016. Thedata output on DIO comes from the TDO output of the JTAG circuit 1614.The JTAG circuit 1614 is timed by the TCK output from controller 2008 toinput the TDI and TMS signals from register 2016 and to output the TDOsignal to I/O circuit 2004 during JTAG data and instruction scanoperations. The JTAG circuit 1614 is reset by the master reset (MRST)output of MRS circuit 2004, which drives the TRST input of the JTAGcircuit 1614. The SPC serves to serialize the JTAG communication betweenthe tester and the JTAG circuit 1614 using the DIO 2004 and CLK 2006signals. Using the two signal DIO and CLK interface of the SPC a testerwould only need two contacts to each integrated circuit being tested inparallel.

FIG. 22 illustrates an example of an integrated circuit 2200 having theJTAG circuit 1802 interfaced to cores 1-N 1502-1506 as describedpreviously in regard to FIG. 18. The TDI, TMS, TCK, TDO, and TRSTinterface signals of the JTAG circuit 1802 are interfaced to the SPCcircuit 2002 as described in FIGS. 20 and 21. The SPC 2002 communicateswith a tester via the external DIO and CLK signals as described in FIGS.20 and 21.

FIG. 23 illustrates in more detail the SPC circuit 2002, JTAG circuit1802, and core circuits 1-N of FIG. 22. The structure and operation ofthe SPC circuit 2002 to serialize the JTAG communication between theJTAG circuit 1802 and the tester, via the DIO and CLK signals, is thesame as described in FIG. 21. The structure and operation of the JTAGcircuit 1802 to enable the cores for testing via the TE 1-N signals isthe same as described in FIG. 18. FIGS. 22 and 23 are provided toillustrate that multiple cores 1502-1506 within an integrated circuit2200 can enabled and tested as described in FIG. 18 using the SPC's DIO2004 and CLK 2006 interface to a tester.

FIG. 24 illustrates a tester 2400 coupled to the scan input 303, scanclock 216, test enable 212, and scan out 304 signals of the testarchitecture of a core 2402 of an integrated circuit 2404 via aninterface 2406. The interface 2406 may represent; (1) the interface ofthe signals to the tester as shown in FIG. 3 (i.e. unidirectionalinterface), (2) the interface of the signals to the tester as shown inFIG. 12 (i.e. differential interface), the interface of the signals tothe tester as shown in FIG. 13 (i.e. SBT interface), the interface ofthe signals to the tester as shown in FIGS. 16-19 (i.e. JTAG interface),or the interface of the signals to the tester as shown in FIG. 20-23(i.e. SPC interface). In addition to these mentioned interfaces,interface 2406 may represent other types of interfaces that may be usedto couple the scan input, scan clock, test enable, and scan outputsignals of the test architecture to the tester.

FIG. 25 illustrates an alternate arrangement for using the testarchitecture within an integrated circuit 2500 that includes multipleembedded cores 2502-2506. The alternate arrangement configures the coresto where their stimulus (S) sections 306 and response (R) sections 312are serialized to form a single scan path of stimulus sections and asingle scan path of response sections 312. The header section 308,controller 310, and optional header return section 314 are shown ascircuit block 2508. The serial input to header section 308 is coupled tothe serial output of the stimulus section 306 of the last core 2506 inthe series of cores and the serial output of the optional header returnsection 314 is coupled to the serial input of the response section 312of the last core 2506 in the serial of cores. . While not shown in FIG.25, the control bus output 316 of controller 310 is coupled to theheader sections 308, optional header return section 314, and to the scanpaths 202, stimulus sections 306, and response sections 312 of each core2502-2506 as shown in FIG. 24 and other Figures. The scan clock 216 andtest enable 212 signals from the tester are input to the controller 310as shown in FIG. 4.

During test, the controller 310 receives and responds to the scan clock216 and test enable input 212 to output control on control bus 316 tooperate the core scan paths 202, core stimulus sections 306, coreresponse sections 312, the header section 308, and the optional headerreturn section 314 as previously described in FIGS. 6-11. To the tester2410, the series of core stimulus sections 306 appear as one longstimulus section and the series of core response sections 312 appear asone long response section. The tester 2410 transmits scan input framesto the series of core stimulus sections 306 and header section 308 viathe scan input 302 and receives scan output frames from the series ofcore response sections 312 and optional header return section 314 viathe scan output 304. The core test arrangement of FIG. 25 differs fromthe core test arrangement in FIG. 15 in that; (1) all cores 2502-2506are enabled for testing by a single test enable 212 input from thetester, and (2) all cores 2502-2506 are tested at the same time by thetester inputting scan input frames on scan input 302 and outputting scanoutput frames on scan output 304.

As previously mentioned in FIG. 24, the interface 2406 of FIG. 25 mayrepresent; (1) the interface of the signals to the tester as shown inFIG. 3 (i.e. unidirectional interface), (2) the interface of the signalsto the tester as shown in FIG. 12 (i.e. differential interface), theinterface of the signals to the tester as shown in FIG. 13 (i.e. SBTinterface), the interface of the signals to the tester as shown in FIGS.16-19 (i.e. JTAG interface), the interface of the signals to the testeras shown in FIG. 20-23 (i.e. SPC interface), or other types ofinterfaces that may be used to couple the scan input 302, scan clock216, test enable 212, and scan output 304 signals of the testarchitecture to the tester 2410.

FIG. 26 is provided to illustrate that the interface of the integratedcircuit test architecture of FIG. 25 may be modified to include morethat one scan input (SI) from a tester and more than one scan output(SO) to a tester. As seen, the serial input to each stimulus inputsection 306 of each core is coupled, via interface 2602, to the tester2600 via a SI 2604-2608 and the serial output from each response section312 is coupled, via interface 2602, to the tester 2600 via a SO2612-2616. Having separate SIs allows the tester to load scan inputframes into the core stimulus sections 306 in parallel. Having separateSOs allows the tester to unload scan output frames from the coreresponse sections 312 in parallel. The ability to load the stimulussections 306 and unload the response sections 312 in parallel decreasesthe time it takes for the tester to input scan frames to and output scanframes from the test architecture, which decreases the time it takes totest the integrated circuit 2601.

For example if each stimulus section 306 and each response section 312of FIG. 25 were 16 bits in length, each scan input and output frameoperation would require 51 bits, i.e. 3×16 bits plus the 3 headersection bits. Using the same 16 bit stimulus 306 and response 312sections and the separate SIs and SOs of FIG. 26, scan input and outputframe operations would only required 19 bits, i.e. 16 bits plus the 3header bits. As seen, the header section 308 and optional header returnsection 314 may use a separate scan input 2610 and scan output 2618respectively if desired, which would further reduce the scan input andoutput frame operations to only 16 bits. The only changes to the tester2600 and the interface circuit 2602 is an increase the number of scaninputs and scan outputs to the integrated circuit 2601.

The interface 2602 of FIG. 26 between the tester 2600 and the testarchitecture may utilize unidirectional input and output signals asshown in FIG. 3, differential input and output signals as shown in FIG.12, or other types of signaling interfaces to couple the testarchitecture's scan inputs 2604-2608, scan clock 216, test enable 212,and scan outputs 2612-2616 to the tester 2600.

FIG. 27 is provided to illustrate that the test architecture of anindividual core 2704 within an integrated circuit 2702 may be modifiedto include more that one scan input (SI) from a tester 2600 and morethan one scan output (SO) to a tester 2600. In FIG. 27 the core scanpaths 202 have been broken up into core scan path groups 2706-2710, witheach group containing a portion of the total number of core scan paths202. Each scan path group has a separate stimulus section 2706-2710 anda separate response section 2712-2716. The serial input to each stimulussection 2706-2710 is coupled, via interface 2602, to the tester 2600 viaa separate scan input signal 2604-2608, and each serial output from eachresponse section 2712-2716 is coupled, via interface 2602, to the tester2600 via a separate scan output signal 2612-2616 signal.

As described by example in regard to FIG. 26, having separate scaninputs to the stimulus sections and separate scan outputs from theresponse sections allows the tester to more quickly load scan inputframes to the test architecture and unload scan output frames from thetest architecture, which reduces test time. As mentioned in FIG. 26, theheader section 308 and optional header return section 314 may use aseparate scan input 2610 and scan output 2618 respectively if desired,which would further reduce the time it takes to perform scan input andoutput frame operations. Also as mentioned in FIG. 26, the interface2602 between the tester 2600 and the test architecture may utilizeunidirectional input and output signals as shown in FIG. 3, differentialinput and output signals as shown in FIG. 12, or other types ofsignaling interfaces to couple the test architecture's scan inputs2604-2608, scan clock 216, test enable 212, and scan outputs 2612-2616to the tester 2600.

While the FM signal of FIGS. 24-27 are shown coming from the headersection 308, it could come from another circuit within the integratedcircuit as mentioned in regard to FIG. 14A or from the tester via anadditional external signal as mentioned in regard to FIG. 14B.

Although exemplary embodiments of the present disclosure have beenillustrated and described above, this does not limit the scope of thepresent disclosure, which can be practiced in a variety of embodiments.

What is claimed is:
 1. A test architecture within an integrated circuitcomprising: (a) a differential data input buffer having differentialinputs and a serial data output; (b) a differential data output bufferhaving a serial data input and differential outputs; (c) logic circuitryhaving parallel stimulus data inputs and parallel response data outputs;(d) parallel scan paths having serial scan inputs for receiving stimulusdata, serial scan outputs for outputting response data, parallelstimulus data outputs coupled to the parallel stimulus data inputs, andparallel response data inputs coupled to the parallel response dataoutputs; (e) an input shift register having a serial shift input coupledto the serial data output, and parallel outputs coupled to the serialscan inputs; and (f) an output shift register having parallel inputscoupled to the serial scan outputs and a serial output coupled to theserial data input.
 2. The test architecture of claim 1 in which theinput shift register includes a flip flop coupled to each paralleloutput.
 3. The test architecture of claim 1 in which the output shiftregister includes a flip flop coupled to each parallel input.
 4. Thetest architecture of claim 1 in which the input shift register includesshift elements having shift inputs connected in series to the serialshift input, a shift element includes a multiplexer having a serial datainput coupled to a shift input, a fixed logic level input, and anoutput, the shift element includes a flip-flop having an input connectedto the output of the multiplexer and an output coupled to a serial scaninput and coupled to a shift output.